The field of application of the invention is the measurement of force transmitted by force transmission equipment. The force transmission equipment is preferably a bicycle chain, in which case the invention measures the force exerted by a bicyclist through pedals to the chain.
The measurement of the force exerted by a bicyclist to a bicycle during pedaling is an interesting field of application for both an occasional bicyclist and an active sports enthusiast. By means of the measurement results, it is, among other things, possible to obtain information on the cycling technique of the bicyclist and to observe the strain of the cycling performance and through this, to plan the ratio between the exercise and the strain. The definition of cycling power and strength is further advantageous for instance for long-lasting exercises aimed at losing weight, in which case the fitness enthusiast tries to perform the fitness performance at a power level below a certain threshold value. The measurement of the force transmitted by the chain is further an important field of application for instance in motorcycles, in which case it is possible by means of the force transmitted by the chain to estimate the motor load, fuel consumption and mechanical wear.
In prior art solutions, the force of the force transmission equipment, such as a chain, has been measured using a method, in which the force has been estimated utilizing the mechanical vibration of the chain caused by the movement of the bicycle, the vibration being generated to the chain for instance by the friction between the chain and cogwheels and the roughness of the cycling surface. It is clear that the prior art solution for defining the force transmission equipment vibration and, further, the force is inaccurate, since the measurement is done indirectly and in a unit separate from the chain.
It is an object of the invention to implement an improved method and an apparatus implementing the method for measuring the force transmitted by force transmission equipment, i.e. the tensile stress affecting the force transmission equipment. This object is achieved by the method described in the following. It is a method for measuring the force transmitted by force transmission equipment, in which method the force transmission equipment is arranged to be a closed loop so that it is connected to a first turning means and from the first turning means to a separate second turning means, and the turning of the first turning means by a power source causes force to transmit by means of the force transmission equipment to the second turning means, turning the second turning means in the same direction as the first turning means. In the method, a reading device separate from the force transmission equipment reads the resonance frequency of a vibration transducer in the force transmission equipment, the resonance frequency being dependent on the level of the force transmitted by the force transmission equipment, and on the basis of the read resonance frequency, calculation means connected to the reading device calculate the force transmitted by the force transmission equipment.
The invention also relates to an arrangement for measuring the force transmitted by force transmission equipment, comprising force transmission equipment in a closed loop and a first turning means connected to the force transmission equipment and a second turning means separate from the first turning means and connected to the force transmission equipment, the turning of the first turning means by a power source causing force to transmit by means of the force transmission equipment to the second turning means, turning the second turning means in the same direction as the first turning means. The force transmission equipment comprises a vibration transducer for establishing a resonance frequency proportional to the force transmitted by the force transmission equipment, and the arrangement comprises a reading device structurally separate from the force transmission equipment for reading the resonance frequency of the vibration transducer, and the arrangement further comprises calculation means connected to the reading device for calculating the force transmitted by the force transmission equipment on the basis of the resonance frequency of the vibration transducer.
The invention also relates to a bicycle which comprises as its force transmission equipment a chain for transmitting the muscular strength of the person pedaling the bicycle from the person to the bicycle to move the bicycle. The bicycle chain has a vibration transducer which is arranged to vibrate at a resonance frequency proportional to the force transmitted by the chain, and the bicycle comprises a reading device separate from the chain for reading the resonance frequency of the vibration transducer, and calculation means connected to the reading device calculate the force affecting the chain on the basis of the resonance frequency.
The invention also relates to a vibration transducer for use in measuring the tensile stress transmitted by force transmission equipment. The vibration transducer intended to be fastened to the force transmission equipment is arranged to receive an electromagnetic excitation and to vibrate at a resonance frequency proportional to the tensile stress affecting the force transmission equipment, the resonance frequency being wirelessly readable for use in calculating the tensile stress transmitted by the force transmission equipment.
Preferred embodiments of the invention are disclosed in the dependent claims.
The invention thus relates to a method and apparatus for measuring the force transmitted by force transmission equipment. The force transmission equipment is arranged in a closed loop. In the description of the invention, force transmission equipment preferably refers to a chain of a bicycle, tricycle, motorcycle or the like. The arrangement of the invention comprises a first turning means and a second turning means separate from the first turning means and connected to the force transmission equipment. A turning means refers preferably to a cogwheel to which the chain can be connected. The forward turning means is then a forward cogwheel to which the bicycle pedals are connected and the second turning means is a cogwheel of the rear wheel. Turning the first turning means by a power source causes force to transmit by means of the force transmission equipment to the second turning means, turning the second turning means in the same direction as the first turning means, i.e. in the case of a bicycle, the force produced by a person through pedals is transmitted through the first cogwheel to the chain and on to the rear cogwheel and the rear wheel. In the solution of the invention, the force transmission equipment has a vibration transducer attached to it and arranged to establish a vibration signal proportional to the force transmitted by the force transmission equipment. The arrangement further comprises a reading device for reading the vibration signal of the vibration transducer proportional to the force as the vibration transducer passes by or through the reading device. In a preferred embodiment of the invention, the arrangement also calculates the power produced by the force transmission equipment by means of the measured force and the rate of movement or velocity of the force transmission equipment.
In a preferred embodiment of the invention, the force transmission equipment is a chain comprising chain pieces, the invention being in no way restricted to the number of the chain pieces. The structure of a chain piece is as known and comprises side plates and axle openings at both ends of the side plates. The chain pieces can be connected to each other by means of axle pins placed in the axle openings in such a manner that the first and second end of each chain piece is connected to different chain pieces. In a preferred embodiment, the vibration transducer measuring the vibration of the chain is located in the axle pin. According to another preferred embodiment, the vibration transducer is located in the side plate of the chain piece. The vibration transducer is preferably electrically insulated from the metal chain for instance by making the chain piece, which comprises the vibration transducer, of carbon fibber resin, ceramics or plastic.
In a preferred embodiment of the invention, the vibration transducer is a resonance circuit implemented as a coil capacitor circuit (LC circuit), for instance. According to a preferred embodiment of the invention, the coil is wound around the side plate of an extension piece and the capacitor is placed close to the coil, in the side plate, for instance. The resonance frequency of the vibration transducer then changes as a function of the force affecting the force transmission equipment because of the change in the capacitor capacitance and/or coil inductance of the resonance circuit. The arrangement for measuring the force of the chain further comprises a reading device, which is structurally, i.e. physically, separate from the force transmission equipment and which is connected to the vibration transducer through an electromagnetic connection for the purpose of reading the resonance/vibration frequency of the vibration transducer. The reading device comprises transmission means for transmitting an electromagnetic excitation to the vibration transducer and reception means for reading the resonance frequency of the vibration transducer. Said means are preferably implemented as coils, whereby the transmission coil oscillates in wide-band thus finding for the vibration transducer a resonance frequency proportional to the force and characteristic to that particular moment, while the reception coil reads the frequency in question. Said properties of the reading device can naturally also be implemented using one coil. The arrangement further comprises calculation means connected to the reading device for establishing from the resonance frequency read by the reading device the tensile stress exerted to the force transmission equipment. In the case of a bicycle, for instance, the reading device is located in the bicycle frame, whereby the vibration transducer and reading device can interact electromagnetically when the vibration transducer passes by or through the reading device.
The method of the invention defines the steps by which the force transmitted by the arrangement of the invention described above is measured.
The invention provides the advantage that the measuring arrangement is simple and thus also easy to install and inexpensive to manufacture in large series. The apparatus according to the method also provides an accurate force and power measurement, when the measurement is made by means of a vibration transducer in a chain.